Covalently bound monolayer for a protective carbon overcoat

ABSTRACT

A magnetic data storage medium may include a substrate, a magnetic recording layer, a protective carbon overcoat, and a monolayer covalently bound to carbon atoms adjacent a surface of the protective carbon overcoat. According to this aspect of the disclosure, the monolayer comprises at least one of hydrogen, fluorine, nitrogen, oxygen, and a fluoro-organic molecule. In some embodiments, a surface of a read and recording head may also include a monolayer covalently bound to carbon atoms of a protective carbon overcoat.

SUMMARY

In one aspect, the present disclosure is directed to an articleincluding a protective carbon overcoat and a monolayer covalently boundto carbon atoms of the protective carbon overcoat. According to thisaspect of the disclosure, the monolayer comprises at least one ofhydrogen, fluorine, nitrogen, oxygen, or a fluoro-organic molecule.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a hard disc drive.

FIG. 2 is a simplified cross-sectional diagram of an example magneticstorage medium.

FIG. 3 is a block diagram illustrating a portion of system including aportion of an example read/write head and a portion of an examplemagnetic storage medium.

FIG. 4 is a block diagram illustrating an example system for depositinga monolayer onto a surface of a magnetic storage medium.

FIG. 5 is a flowchart illustrating an example process for depositing amonolayer onto a surface of a magnetic storage medium.

FIG. 6 is a graph of force versus separation of a firstcarbon(100)-hydrogen surface and a second carbon(100)-hydrogen surface.

FIG. 7 is a graph of friction force versus applied load for a firstcarbon(100)-hydrogen surface and a second carbon(100)-hydrogen surface.

DETAILED DESCRIPTION

Some magnetic data storage media include a carbon protective overcoatformed on the magnetic recording layer and a lubricant layer depositedon the carbon protective overcoat. In some embodiments, the lubricantlayer may include a thickness between approximately 0.5 nanometers (nm)and approximately 2 nm and provides a coefficient of friction ofapproximately 0.1 between the surface of the carbon protective overcoatand a surface of a recording and read head. In some cases, thisthickness may be greater than desired.

For example, it may be desirable to decrease the flying height of amagnetic recording and read head over the magnetic storage medium infuture magnetic data storage devices to an in-contact or a nearlyin-contact flying height in order to improve a signal-to-noise ratio ofthe system. Reducing the flying height of the recording and read headmay reduce the distance between the magnetic transducer of the recordingand read head and the magnetic domains of the magnetic storage medium,and thus may increase the magnetic field strength detected by the readhead for the same magnetization of the magnetic domains of the magneticstorage medium. Use of some lubricants in the head-media system mayresult in excessive friction between the recording and read head and themagnetic storage medium at these low flying heights and may lead to highwear rates, resulting in damage to and the eventual failure of a surfaceof the magnetic storage medium, a surface of the recording and readhead, or both.

One option for reducing the head-media spacing is to forgo use of alubricant layer and leave an uncoated protective carbon overcoat as thecontact surface between the magnetic storage medium and the recordingand read head. However, with no additional coating, such an interfaceresults in a coefficient of friction that ranges from about 0.2 to about0.5. Such a value for the coefficient of friction may lead to excessivewear at the interface of the recording and read head and the magneticstorage medium, or even premature failure of the magnetic storagemedium, recording and read head, or both.

In general, the present disclosure is directed to a magnetic datastorage medium and, optionally, a magnetic recording and read head,including a protective carbon overcoat surface covalently bound to amonolayer of molecules, which may reduce a coefficient of friction ofthe surface compared to an untreated carbon protective overcoat surface.Additionally, the monolayer may facilitate a reduction of a flyingheight of the recording and read head over a surface of the magneticdata storage medium. The covalently-bound molecules may include, forexample, hydrogen, fluorine, nitrogen, oxygen, a fluoro-organicmolecule, or the like. The disclosure also presents a method fordirectly depositing the monolayer of molecules onto the surface ofcarbon protective overcoat. Carbon overcoat surfaces treated in thismanner may have a lower or even significantly lower coefficient offriction and a lower wear rate compared to uncoated surfaces or surfacescoated with a separate lubricant layer.

FIG. 1 illustrates an exemplary magnetic disc drive 100, which mayinclude a magnetic data storage medium 108 having an ultra-low frictionovercoat according to one aspect of the present disclosure. Disc drive100 includes base 102 and top cover 104, shown partially cut away. Base102 combines with top cover 104 to form the housing 106 of disc drive100. Disc drive 100 also includes one or more rotatable magnetic datastorage media 108. Magnetic storage media 108 are attached to spindle114, which operates to rotate media 108 about a central axis. Magneticrecording and read head 112 is adjacent to magnetic storage media 108.Actuator arm 110 carries magnetic recording and read head 112 forcommunication with each of the magnetic storage media 108.

Magnetic storage media 108 store information as magnetically orientedbits in a magnetic recording layer. Magnetic recording and read head 112includes a recording (write) head that generates magnetic fieldssufficient to magnetize discrete domains of the magnetic film onmagnetic storage media 108. These discrete domains of the magnetic filmeach represent a bit of data, with one magnetic orientation representinga “0” and a substantially opposite magnetic orientation representing a“1.” Magnetic recording and read head 112 also includes a read head thatis capable of detecting the magnetic fields of the discrete magneticdomains of the magnetic film.

According to one aspect of the present disclosure, magnetic storagemedia 108 may not include a lubricant layer deposited on a surface of aprotective carbon overcoat. Instead, magnetic storage media 108 mayinclude a monolayer of molecules or atoms covalently bound to carbonatoms adjacent a surface of the protective carbon overcoat. Themonolayer of molecules or atoms may reduce a coefficient of friction ofthe surface compared to an untreated carbon protective overcoat surface,and may facilitate a reduction in the flying height of recording andread head 112 over the surface of a magnetic storage media 108.

FIG. 2 is a simplified cross-sectional diagram of an exemplary magneticstorage medium 108. For purposes of illustration, magnetic storagemedium 108 is a perpendicular recording medium. However, in otherexamples, the monolayer disclosed herein may be utilized with anothertype of recording medium, such as, for example, a longitudinal recordingmedium, a heat-assisted magnetic recording (HAMR) medium, a wireassisted magnetic recording (WAMR) medium, or the like. In embodimentillustrated in FIG. 2, magnetic storage medium 108 includes a substrate122, soft underlayer (SUL) 124, a first interlayer 126, a secondinterlayer 128, a magnetic recording layer 130, a protective carbonovercoat 132, and a monolayer 134 covalently bound to carbon atomsadjacent an upper surface 136 of protective carbon overcoat 132.

Substrate 120 may include any material that is suitable to be used inmagnetic recording media, including, for example, Al, NiP plated Al,glass, ceramic glass, or the like.

Although not shown in FIG. 2, in some embodiments, at least oneadditional underlayer may be present immediately on top of substrate120. The additional underlayer may be amorphous and provides adhesion tothe substrate and low surface roughness.

A soft underlayer (SUL) 124 is formed on substrate 120 (or theadditional underlayer, if one is present). SUL 124 may be any softmagnetic material with sufficient saturation magnetization (B_(S)) andlow anisotropy (H_(k)). For example, SUL 124 may be an amorphous softmagnetic material such as Ni; Co; Fe; an Fe-containing alloy such asNiFe (Permalloy), FeSiAl, FeSiAlN, or the like; a Co-containing allowsuch as CoZr, CoZrCr, CoZrNb, or the like; or a CoFe-containing alloysuch as CoFeZrNb, CoFe, FeCoB, FeCoC, or the like.

First interlayer 126 and second interlayer 128 may be used to establishan HCP (hexagonal close packed) crystalline orientation that induces HCP(0002) growth of the magnetic recording layer 130, with a magnetic easyaxis perpendicular to the plane of magnetic storage medium 108.

Magnetic recording layer 130 may include Co alloys. For example, the Coalloy may include Co in combination with at least one of Cr, Ni, Pt, Ta,B, Nb, O, Ti, Si, Mo, Cu, Ag, Ge, or Fe. Magnetic recording layer 130may also include a Fe—Pt alloy, a Sm—Co alloy, or the like. In someembodiments, magnetic recording layer 130 may include a non-magneticoxide, such as SiO₂, TiO₂ CoO, Cr₂O₃, Ta₂O₅, or the like, whichseparates the magnetic grains.

A protective carbon overcoat 132 may be formed on magnetic recordinglayer 130. Protective carbon overcoat 132 may include, for example,diamond like carbon, which has a crystal lattice similar to diamond, oran amorphous carbon layer. In some embodiments, an upper surface 136 ofprotective carbon overcoat 132 may comprise a (100) crystal plane. Inother embodiments, upper surface 136 may comprise another crystal plane.

Carbon atoms adjacent upper surface 136 of protective carbon overcoat132 may be covalently bound to respective molecules of monolayer 134. Inthe present disclosure, adjacent to upper surface 136 is defined as theplane or planes of atoms exposed at upper surface 136 and available tobond to a molecule or atom in monolayer 134. Monolayer 134 may comprisemolecules or atoms that reduce a coefficient of friction with anothersurface compared to a coefficient of friction between an untreated uppersurface 136 of protective carbon overcoat 132 and the other surface.

In some embodiments, monolayer 134 may eliminate the need for a separatelubricant layer, which in some systems is formed on upper surface 136 ofprotective carbon overcoat 132. Monolayer 134 may provide upper surface136 with sufficiently low friction that a separate lubricant layer isnot required on upper surface 136.

Because a separate lubricant layer is not required, use of monolayer 134may reduce a flying height of a recording and read head 112 overmagnetic storage medium 108. Monolayer 134 may have a thickness betweenapproximately 0.9 Å and approximately 5 Å. This may be thinner than thethickness of a separate lubricant layer applied to upper surface 136 ofprotective carbon overcoat 132. The relative thinness of monolayer 134compared to a separate lubricant layer may facilitate a lower flyingheight of recording and read head 112 over upper surface 136 ofprotective carbon overcoat 134.

A lower flying height of recording and read head 112 over upper surface136 of protective carbon overcoat 134 may increase a signal-to-noiseratio (SNR) of magnetic disc drive 100. For example, reducing the flyingheight of recording and read head 112 may reduce the distance betweenthe magnetic transducer of the recording and read head 112 and themagnetic domains of the magnetic storage medium 108. This may increasethe magnetic field strength detected by the recording and read head 112for the same magnetization of the magnetic domains of the magneticstorage medium 108. The increased magnetic field strength may result inread head 112 generating an increased signal, and an increasedsignal-to-noise ratio.

Similarly, a decreased flying height of recording and read head 112 mayincrease the recording performance of magnetic disc drive 100. To recordinformation to magnetic storage medium 108, a recording transducer inrecording and read head 112 may generate a magnetic field with aspecific orientation, which induces a magnetic orientation in domainswithin magnetic recording layer 130. By reducing the flying height ofrecording and read head 112, spacing between the recording transducer inrecording and read head 112 and magnetic recording layer 130 may bereduced. This may increase the strength of the magnetic field at themagnetic recording layer 130 (for the same magnetic field generated bythe recording transducer). This may allow magnetic recording layer 130to comprise materials with increased coercivity, which may increasestability of the magnetic domains, or may allow other improvements tothe recording system, such as use of other recording transducers.

In some embodiments, monolayer 134 may comprise a plurality of moleculeseach covalently bound to a respective carbon atom adjacent the uppersurface 136 of protective carbon overcoat 132. For example, monolayer134 may include a plurality of fluoro-organic molecules, e.g., —CF,—CF₂, —CF₃, —CF₂—CF₃, —CF₂—CF₂—CF₃, or —CF₂—CF₂—CF₂—CF₃, each covalentlybound to a respective carbon atom adjacent upper surface 136.

In other embodiments, monolayer 134 may comprise a plurality of singleatoms each covalently bound to a respective carbon atom adjacent theupper surface 136 of protective carbon overcoat 132. For example,monolayer 134 may comprise at least one of hydrogen, nitrogen, oxygen,or fluorine. In some embodiments, a monolayer 134 comprising singleatoms covalently bound to protective carbon overcoat 132 may be thinnerthan a monolayer 134 comprising molecules bound to protective carbonovercoat 132. In this way, a monolayer 134 including single atomscovalently bound to protective carbon overcoat 132 may facilitate asmaller flying height than a monolayer 134 including moleculescovalently bound to protective carbon overcoat 132.

Monolayer 134 may be deposited on upper surface 136 in a vacuum chamberusing a plasma source, such as, for example, a radio-frequency inductiveplasma source, a radio-frequency capacitive plasma source, a DC arcplasma source, a hollow cathode plasma source, microwave plasma sourceor an electron cyclotron resonance (ECR) plasma source, as described infurther detail with respect to FIGS. 4 and 5.

Monolayer 134 preferably substantially fully covers upper surface 136 ofprotective carbon overcoat 132. In other words, preferably substantiallyall of the carbon atoms adjacent upper surface 136 are covalently boundto a molecule or atom in monolayer 134. In some embodiments, uppersurface 136 may comprise approximately 10¹⁵/cm² surface bonding sites(e.g., 10¹⁵ exposed carbon atoms adjacent to upper surface 136 andavailable for bonding to atoms or molecules in monolayer 134). Onemeasure of the coverage coverage of upper surface 136 is the coveragedensity, which is defined as nanograms (ng) of monolayer 134 percentimeter squared (cm²) of upper surface 136. The coverage density mayvary depending on the atom or molecule in monolayer 134. In someembodiments, monolayer 134 may comprise a coverage density of less thanapproximately 400 nanograms per cm² (ng/cm²). In other embodiments,monolayer 134 may comprise a coverage density of between approximately200 ng/cm² and approximately 400 ng/cm². In some examples, a monolayer134 comprising, for example, hydrogen atoms may have a lower coveragedensity than a monolayer 134 comprising a fluoro-organic molecule, suchas —CF₂—CF₂—CF₂—CF₃.

In some embodiments, not all the carbon atoms adjacent to upper surface136 may be covalently bonded to a molecule in monolayer 134. Forexample, when monolayer 134 comprises a chain molecule, such as—CF₂—CF₂—CF₂—CF₃ or the like, the number of carbon atoms that arecovalently bonded to a —CF₂—CF₂—CF₂—CF₃ may be less than 10¹⁵/cm². Forexample, only approximately 5×10⁷/cm² carbon atoms may be covalentlybound to a —CF₂—CF₂—CF₂—CF₃, and monolayer 134 may still effectivelyreduce friction of upper surface 136 compared an uncoated upper surface136 or a separate lubricant layer. Accordingly, in some embodiments,between approximately 50 percent and 100 percent of carbon atomsadjacent to upper surface 136 may be bound to an atom or molecule inmonolayer 134. The desired surface density of covalently bound surfacesites may depend on the atom or molecule in monolayer 134. For example,a surface density of covalently bound surface sites of —CF₂—CF₃ may beless than a surface density of covalently bound surface sites of —H, —F,or the like. Similarly, a surface density of covalently bound surfacesites of —CF₂—CF₂—CF₃ may be less than a surface density of covalentlybound surface sites of —CF₂—CF₃.

In some embodiments, such as, for example, when monolayer 134 compriseshydrogen, monolayer 134 may be thermally stable up to approximately 900°C. Additionally or alternatively, monolayer 134 may be substantiallynon-wetting, forming a water contact angle of approximately 95°, and mayhave relatively low chemical reactivity.

Although is some embodiments only upper surface 136 of magnetic storagemedium 108 is covalently bound to monolayer 134, in other embodiments, asurface of recording and read head 112 may also be covalently bound to amonolayer. FIG. 3 is a block diagram illustrating a portion of such asystem including a portion of an example recording and read head 112 anda portion of an example magnetic storage medium 108. Upper surface 136of magnetic storage medium 108 and lower surface 142 of recording andread head 112 are covalently bound to a first monolayer 134 and a secondmonolayer 140, respectively.

Similar to magnetic storage medium 108, recording and read head 112 mayinclude a protective carbon layer 138, which defines lower surface 142.Protective carbon layer 138 may form a surface of at least an advancedair bearing (AAB) slider portion of recording and read head 112.Protective carbon overcoat 138 may include, for example, diamond likecarbon or an amorphous carbon layer. In some embodiments, lower surface142 of protective carbon overcoat 138 may comprise a (100) crystalplane. In other embodiments, lower surface 142 may comprise anothercrystal plane.

Carbon atoms adjacent lower surface 142 of protective carbon overcoat138 may be covalently bound to respective molecules of second monolayer140. In the present disclosure, adjacent to lower surface 142 is definedas the plane or planes of atoms exposed at lower surface 142 andavailable to bond to a molecule or atom in second monolayer 140. Secondmonolayer 140 may comprise molecules or atoms that reduce a coefficientof friction with another surface (e.g., upper surface 136 of firstprotective carbon overcoat 132) compared to a coefficient of frictionbetween an untreated lower surface 142 and the other surface.

Second monolayer 140 may have a thickness between approximately 0.9 Åand approximately 5 Å. The thickness of second monolayer 140 mayfacilitate a low flying height of recording and read head 112 over uppersurface 136 of protective carbon overcoat 134.

In some embodiments, second monolayer 140 may comprise a plurality ofmolecules each covalently bound to a respective carbon atom adjacentupper surface 142 of protective carbon overcoat 138. For example, secondmonolayer 140 may include a plurality of fluoro-organic molecules eachcovalently bound to a respective carbon atom adjacent lower surface 142.

In other embodiments, second monolayer 138 may comprise a plurality ofsingle atoms each covalently bound to a respective carbon atom adjacentlower surface 142 of protective carbon overcoat 138. For example, secondmonolayer 140 may comprise at least one of hydrogen, nitrogen, oxygen,or fluorine. In some embodiments, a second monolayer 140 comprisingsingle atoms covalently bound to protective carbon overcoat 138 may bethinner than a second monolayer 140 comprising molecules bound toprotective carbon overcoat 138. In this way, a second monolayer 140including single atoms covalently bound to protective carbon overcoat138 may facilitate a smaller flying height than a second monolayer 140including molecules covalently bound to protective carbon overcoat 138.

In some embodiments, second monolayer 140 may include the same species(atom or molecule) as first monolayer 134. In other embodiments, secondmonolayer 140 may include a different species (atom or molecule) thanfirst monolayer 134.

Second monolayer 140 may be deposited on lower surface 142 in a vacuumchamber using a plasma source, such as, for example, a radio-frequencyinductive plasma source, a radio-frequency capacitive plasma source, aDC arc plasma source, a hollow cathode plasma source, microwave plasmasource or an electron cyclotron resonance (ECR) plasma source, asdescribed in further detail below with respect to FIGS. 4 and 5.

Second monolayer 140 preferably substantially fully covers lower surface138 of protective carbon overcoat 138. In other words, substantially allof the carbon atoms adjacent lower surface 138 are preferably covalentlybound to a molecule or atom in second monolayer 140.

Use of second monolayer 140 may further decrease friction between uppersurface 136 and lower surface 142 compared to an uncoated lower surface142 and a coated upper surface 136 or an uncoated lower surface 142 andan uncoated upper surface 136. For example, the coefficient of frictionbetween upper surface 136 covalently bound to first monolayer 134 andlower surface 142 covalently bound to second monolayer 140 may be lessthan approximately 0.02. In some embodiments, the coefficient offriction between upper surface 136 covalently bound to first monolayer134 and lower surface 142 covalently bound to second monolayer 140 maybe less than approximately 0.002, or even less than approximately0.0002. A low coefficient of friction may reduce a wear rate of uppersurface 136, lower surface 142, or both, and may extend a lifetime ofrecording and read head 112 and/or magnetic storage medium 108.

FIG. 4 is a block diagram illustrating an example system for depositinga monolayer onto a surface of a magnetic storage medium or a recordingand read head. For purposes of illustration, FIG. 4 will be describedwith concurrent reference to FIG. 5, which is a flowchart illustratingan example process for depositing a monolayer onto a surface of amagnetic storage medium or a recording and read head.

The deposition system 152 illustrated in FIG. 4 includes a vacuumchamber 160, an ionization source 156, and a gas input line 154.Positioned within vacuum chamber 160 is a magnetic storage medium 108,which may be similar to magnetic storage medium 108 described withrespect to FIG. 2. Deposition system 152 also optionally includes ashield 162. In some embodiments, vacuum chamber 160 may be contiguouswith or connected to a chamber in which protective carbon overcoat 132is deposited on magnetic recording layer 130, in order to reduce orminimize contamination of upper surface 136 with unwanted chemicalspecies. Vacuum chamber 160, and more particularly magnetic storagemedium 108, may be maintained at or near room temperature (e.g.,approximately 25° C.) to encourage proper surface chemistry.

As shown in FIG. 5, during the deposition process, an input gas isinjected into the ionization source 156 in vacuum chamber 160 via gasinput line 154 (162). The input gas may include the species to becovalently bound to upper surface 136 of magnetic storage medium 108,e.g., F₂, H₂, N₂, O₂, a fluoro-organic molecule, or the like. In someembodiments, the input gas may also include a carrier gas, such as, forexample, He or Ar. The input gas may be at a low pressure, e.g., on theorder of milliTorrs, and may have a flow rate of between approximately 1standard cubic centimeter per minute (SCCM) and approximately 10 SCCM.The precise pressure and flow rate of the input gas may be selected toproduce the desired coverage of upper surface 136 by monolayer 134 (FIG.2) and to minimize the implantation of the species forming monolayer 134in protective carbon overcoat 132. The operating parameter may alsodepend on the type of plasma source (e.g., a radio-frequency inductiveplasma source, a radio-frequency capacitive plasma source, a DC arcplasma source, a hollow cathode plasma source, microwave plasma sourceor an electron cyclotron resonance (ECR) plasma source) and the geometryof the source.

In some embodiments, shield 162, which may be a thin metal plate, isplaced between ionization source 156 and magnetic storage medium 108 toblock direct bombardment of protective carbon overcoat 132 by ions 158.This may reduce the momentum with which ions 158 approach overcoat 132,and reduces or substantially eliminates implantation of ions 158 inprotective carbon overcoat 132. The size and position of shield 162 maydepend on the size and position of ionization source 156 relative tomagnetic storage medium 108. In some embodiments, the size and positionof shield 162 may be selected such that when viewed from a point onupper surface 136 of magnetic storage medium 108 a solid angle 164 ofionization source 156 is covered. Additionally or alternatively, theflow rate and pressure of the input gas may be selected such that ions158 formed by the ionization source 156 approach upper surface 136 withlow momentum (i.e., velocity), which may minimize implantation of theions 158 in protective carbon overcoat 132.

Ionization source 156 produces ions 158, which are the species that formmonolayer 134 (164). Ionization source 156 may comprise, for example, aradio-frequency inductive plasma source, a radio-frequency capacitiveplasma source, a DC arc plasma source, a hollow cathode plasma source,microwave plasma source or an electron cyclotron resonance (ECR) plasmasource. The beam current of ionization source 156 may be betweenapproximately 10 milliamps (mA) and approximately 100 (mA) and the beamvoltage may be between approximately 100 electron volts (eV) andapproximately 2,000 eV. The particular beam current and beam voltage maybe selected to increase formation of the desired atoms 158 and/or reduceformation of unwanted species.

Ions 158 approach upper surface 136 of magnetic storage medium 108 andcovalently bond to carbon atoms adjacent upper surface 136 to formmonolayer 134 (166). Ions 158 preferably approach upper surface 136 at alow velocity (with little momentum) to reduce the probability ofimplantation of ions 158 in magnetic storage medium 108 or damage toupper surface 136 and increase the probability that ions 158 will reactwith carbon atoms adjacent upper surface 136 to form covalently boundmonolayer 134. As described above, ionization source 156 is preferablyfed sufficient input gas to form sufficient ions 158 to substantiallyfully cover upper surface 136, i.e., substantially every carbon atomadjacent upper surface is bound to an atom or molecule of monolayer 134.

EXAMPLES Examples 1-3

FIG. 6 is an example of a graph of predicted force versus separationdistance of a first surface and a second surface. In FIG. 6, threecurves are shown. Curve 172 illustrates a predicted force versusseparation distance for a first C(100)-H surface and a second C(100)-Hsurface. Curve 174 illustrates a predicted force versus separationdistance for a first C(100)-F surface and a second C(100)-F surface.Curve 176 illustrates a predicted force versus separation distance for afirst C(100)-O surface and a second C(100)-O surface. Each of the curvesshows a potential well (attractive (negative) force) at between about 4Å and about 6 Å. The potential well 178 is largest and occurs at thesmallest separation distance (about 4 Å) for the C(100)-H surfaces. Thepotential wells 180, 182 for the C(100)-F and C(100)-O surfaces,respectively, are smaller in magnitude than potential well 178 and occurat a greater separation distance (about 5.5 Å).

The predicted force curves also show a large repulsive, i.e., positiveforce, occurring at a smaller separation distance that the potentialwell. For example, the C(100)-H surfaces show a large repulsive wall atabout 3.8 Å. The C(100)-F and C(100)-O surface show a large repulsivewall at about 5 Å. This may indicate that C(100)-H surface may allowsmaller flying heights, and thus facilitate a higher SNR, than C(100)-For C(100)-O surfaces.

Example 4

FIG. 7 is a graph of friction force versus applied load for a firstC(100)-H surface and a second C(100)-H surface. By using the calculatedfriction force and the known applied load, the coefficient of frictionfor the two surfaces may be calculated. As FIG. 7 shows, the coefficientof friction as calculated from a four point linear regression was foundto be about 0.000135. Note that a 0.14 (nano-Newton) nN load gives abouta 100 mega-Pascal (MPa) contact pressure.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

The invention claimed is:
 1. An article comprising: a substrate; amagnetic recording layer; a protective carbon overcoat formed on themagnetic recording layer, wherein the surface of the protective carbonovercoat comprises a (100) plane of carbon atoms; and a monolayercovalently bound to carbon atoms of the protective carbon overcoat,wherein the monolayer comprises at least one of hydrogen, fluorine,nitrogen, oxygen, and a fluoro-organic molecule.
 2. The articleaccording to claim 1, wherein the monolayer comprises a thicknessbetween approximately 0.9 Å and approximately 5.0 Å.
 3. The articleaccording to claim 1, wherein the monolayer comprises an atomicmonolayer.
 4. The article according to claim 1, wherein the monolayercomprises at least one of —CF, —CF₂, —CF₃, —CF₂—CF₃, —CF₂—CF₂—CF₃, or—CF₂—CF₂—CF₂—CF₃.
 5. The article of claim 1, wherein the monolayercomprises a coverage density of between approximately 200 ng/cm² andapproximately 400 ng/cm².
 6. The article of claim 1, wherein themonolayer is thermally stable up to approximately 900° C.